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Abstract:

A device for protecting an electrical installation from surges, includes
two terminals, a protective component connected to the terminals, and a
thermal disconnector having a conductive contact blade maintained in a
first position in which the contact blade ensures an electrical
connection between the protective component and one of the two terminals.
The thermal disconnector can be provided for making the contact blade go
to a second position when the temperature of the protective component
exceeds a predetermined threshold, wherein the contact blade and the one
of the two connection terminals are part of a single and same piece.

Claims:

1. A protective device for protecting an electrical installation from
surges, comprising: two connection terminals for connecting the device to
an electrical installation to be protected; a protective component
protecting against overvoltages, said protective component being
electrically connected to the two connection terminals; and a thermal
disconnector comprising a conductive contact blade maintained in a first
position in which the contact blade ensures an electrical connection
between the protective component and one of the two connection terminals,
the thermal disconnector being provided for making the contact blade go
to a second position when the temperature of the protective component
exceeds a predetermined temperature threshold in which second position
said electrical connection is open; wherein the contact blade and said
one of the two connection terminals are part of a single and same piece.

2. The protective device according to claim 1, wherein the protective
component is a varistor.

3. The protective device according to claim 1, comprising: a member for
reducing or eliminating electric arcs which form during movement of the
contact blade from the first position towards the second position, the
reducing or eliminating member being chosen from the group of arc
reducing or eliminating members consisting of electric means, electronic
means, electromechanical means, and mechanical means.

4. The protective device according to claim 1, wherein the piece to which
the contact blade and said one of the two connection terminals belong has
an IACS conductivity greater than or equal to 70%.

5. The protective device according to claim 4, wherein the piece to which
the contact blade and said one of the two connection terminals belong is
made from copper with a copper content greater than or equal to 99.9%.

6. The protective device according to claim 1, wherein the piece formed
by the contact blade and said one of the two connection terminals
comprises: a flexible part intermediate between the contact blade and the
terminal for allowing the contact blade to move relative to the one
connection terminal, between the first position and the second position.

7. The protective device according to claim 1, wherein the contact blade
is elastically stressed towards the second position, the thermal
disconnector comprising: a thermosensitive element in thermal contact
with the protective component, said thermosensitive element being
provided for maintaining the contact blade in the first position up to
the predetermined temperature threshold and for releasing the contact
blade when the temperature of the protective component exceeds the
predetermined temperature threshold.

8. The protective device according to claim 7, wherein the
thermosensitive element is a thermofusible braze by which the contact
blade is welded to a pole of the protective component.

9. The protective device according to claim 8, wherein a part of the
contact blade welded to the pole by the thermofusible braze is connected
to a remainder of the contact blade by a local restriction of a section
of the contact blade to concentrate heat when given off by the protective
component at the thermofusible braze.

10. The protective device according to claim 9, wherein the part of the
contact blade welded to the pole of the protective component is tinned.

11. The protective device according to claim 1, wherein the contact blade
extends primarily in a first plane parallel to a main face of the
protective component, such that movement of the contact blade between the
first position and the second position will occur mainly in said first
plane.

12. The protective device according to claim 1, comprising: a second
thermal disconnector to disconnect the protective component from the
electrical installation when a temperature of the protective component
exceeds another predetermined temperature threshold.

13. The protective device according to claim 1, wherein the piece to
which the contact blade and said one of the two connection terminals
belong has an IACS conductivity greater than or equal to 90%.

14. The protective device according to claim 1, wherein the piece to
which the contact blade and said one of the two connection terminals
belong has an IACS conductivity greater than or equal to 95%.

Description:

RELATED APPLICATION

[0001] This application claims priority under 35 U.S.C. §119 to
French Patent Application No. 1052736 filed in France on Apr. 9, 2010,
the entire content of which is hereby incorporated by reference in its
entirety.

FIELD

[0002] The present disclosure relates to the general technical field of
devices for protecting equipment or electrical installations from
overvoltages, such as from surges, due for example to a lightning strike.
The present disclosure also relates to devices for protecting an
electrical installation from surges, such as a varistor lightning
arrestor, for low-voltage electrical installations.

BACKGROUND INFORMATION

[0003] It is known that the protection of an electrical installation from
overvoltages can be achieved by using devices including at least one
component for protection from overvoltages, for example one or more
varistors and/or one or more spark gaps. For single phase installations,
it is known to use a varistor connected between the phase and the neutral
and a spark gap connected between the neutral and the ground. For
three-phase installations, it is known to position varistors between the
different phases and/or between each phase and the neutral and a spark
gap between the neutral and the ground. For electrical installations
operating under direct current, for example for photovoltaic generator
installations, varistors and possibly spark gaps can be used.

[0004] In the event of failure of the protection component, these known
devices include a disconnection system serving to isolate the protective
component from the electrical installation as a safety measure. For
example, in the case of varistors, it is known to provide thermal
protection. The thermal protection or thermal disconnector can disconnect
the varistor from the electrical installation to be protected in the
event of excessive heating of the varistor, for example beyond
140° C. This excessive heating of the varistor is due to the
increase of the leakage current--generally several tens of
milliamperes--due to its aging, which is known as thermal runaway of the
varistor.

[0005] The thermal disconnector often comprises (e.g., consists of) a
low-temperature weld that keeps a conductive element in place to form a
mobile contact through which the varistor is connected to the electrical
installation, when the conductive element is elastically stressed towards
the opening. The fusion of the weld results in the mobile contact moving
under the effect of the elastic stress, which causes the disconnection of
the varistor. Thermal disconnectors of this type are described in EP-A-0
716 493, EP-A-0 905 839, and EP-A-0 987 803, each of which is hereby
incorporated by reference in its entirety.

[0006] These known devices which protect against overvoltages, and their
thermal disconnector, can be faced with different restrictive situations
during their use. The restrictive situations can depend, for example, on
the type of electrical grid to which they are attached.

[0007] First, their thermal disconnector should have a sufficient
interrupting capacity to effectively disconnect the protection component
in case of thermal runaway. This constraint can be more delicate in the
case of installations operating under direct current, given that there is
no periodic passage at zero volts, as with alternating current. The
alternating current contributes to the extension of the electric arc
generated at the opening of the mobile contact.

[0008] The electrical circuit of the protective devices shall also be able
to support the constraints resulting from electrical shocks, such as the
lightning currents for which they are provided. These electric shocks can
be surges with a significant amplitude (e.g., several thousand volts) and
short duration (e.g., from a microsecond to a millisecond). These
overvoltages, for example, can cause electrodynamic stresses and
temperature increases that mechanically stress the different conductive
pieces making up the protection device. Despite these mechanical
stresses, the electrical circuit ensuring the connection of the
protective component to the electrical installation should remain closed.
In particular, the mechanical stresses should not cause the thermal
disconnector to turn on via pulling out of the thermofusible braze. The
ability of the device to meet this constraint can be verified by the
applicable standards, for example, in installations supplied with
low-voltage alternating current, in paragraph 7.6 (operating duty tests)
of standard IEC 61643-1, 2nd ed., 2005-03 (hereafter noted IEC paragraph
7.6), or paragraph 37 (Surge testing) of standard UL 1449, 3rd ed.,
09.29.2006 (hereafter noted UL paragraph 37). For direct current
installations such as photovoltaic generator installations, examples
include paragraph 6.6 (Operating duty tests) of photovoltaic guide UTE C
61-740-51 dated June 2009 (hereafter UTE paragraph 6.6).

[0009] Moreover, the electric circuit of the protective device connecting
the protective component to the electrical installation can be subject to
very high currents under the nominal voltage of the electrical
installation, for example in installations powered by the alternating
voltage grid. This example occurs when the varistor of the protection
device experiences a power outage by short circuit. In this case, the
disconnection of the failing varistor is caused by a specific protection
from short circuits such as a fuse or a circuit-breaker. Given the
reaction time of this specific protection, the electric circuit of the
protection device, including the thermal disconnector, should not cause
any fire outbreak in that period of time, given the significance of the
short circuit currents provided by the electrical power grid. The ability
of the device to satisfy this constraint can be verified for
installations powered with low-voltage alternating current, for example
in paragraph 7.7.3 (Short circuit withstand) of standard IEC 61643-1, 2nd
ed., 2005-03 (hereafter noted IEC paragraph 7.7.3).

[0010] The device for protection from overvoltages can also be capable of
being powered by a surge related to an anomaly in the voltage of the
power grid of the electrical installation, when a power outage caused by
a short circuit of a varistor if there are at least two varistors
serially connected between the lines of the power grid. In such a case,
the varistor turns on and can pass a very high current given its low
independence. The current is more or less the short circuit current that
the power grid of the electrical installation can supply. Faced with such
a situation, the protective device should not cause a fire to start.

[0012] These protective devices should therefore, depending on the case,
meet a number of constraints. The present disclosure sets forth exemplary
embodiments which can improve the resistance of protective devices to
overvoltages in situations where the protective component, for example
regarding a varistor, reaches the end of its life by short circuit under
nominal voltage, this situation being taken into account by standard IEC
paragraph 7.7.3, as mentioned above. Indeed, specific protection from
overvoltages can have a relatively long reaction time, in the vicinity of
a second or more. There is a risk that during this period of time, the
passage of a high intensity current in the protective device may cause
the formation of an uncontrolled electric arc in the device protecting
from overvoltages. Such an uncontrolled arc can then initiate a fire
outbreak in the electrical installation.

SUMMARY

[0013] A protective device for protecting an electrical installation from
surges is disclosed. The protective device comprises two connection
terminals for connecting the device to an electrical installation to be
protected; and a protective component protecting against overvoltages,
said protective component being electrically connected to the two
connection terminals. The protective device includes a thermal
disconnector that comprises a conductive contact blade maintained in a
first position in which the contact blade ensures an electrical
connection between the protective component and one of the two connection
terminals. The thermal disconnector being provided for making the contact
blade go to a second position when the temperature of the protective
component exceeds a predetermined temperature threshold in which second
position said electrical connection is open, wherein the contact blade
and said one of the two connection terminals are part of a single and
same piece.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Other features and advantages of the disclosure will appear upon
reading the following detailed description of exemplary embodiments of
the disclosure, provided solely for information and with reference to the
appended drawings, as follows:

[0015]FIG. 1 illustrates a perspective view of a protective cartridge of
a low-voltage electrical installation in accordance with an exemplary
embodiment;

[0016] FIGS. 2A, 2B illustrate side and front views of a protective
cartridge in accordance with an exemplary embodiment;

[0017] FIGS. 3A, 3B illustrate an inner volume defined by the case of the
cartridge in accordance with an exemplary embodiment;

[0018]FIG. 4 illustrates a mobile contact of the protective device in the
closed position in accordance with an exemplary embodiment;

[0019] FIGS. 5 and 6 illustrates a mobile contact of the protective device
in the open position and a diagram of the removed part of the case in
accordance with an exemplary embodiment;

[0020] FIG. 7 illustrates a front view of the varistor housed with the
rest of the protective device in the cartridge in accordance with an
exemplary embodiment;

[0021] FIGS. 8A, 8B, and 8C each illustrate a perspective view of an
electrode of the varistor in accordance with an exemplary embodiment;

[0022]FIG. 8D illustrates a profile view of the electrode of the
varistor;

[0023] FIGS. 9 and 10 illustrate a profile and perspective view of an
electrical contact piece in accordance with an exemplary embodiment;

[0024] FIGS. 11A and 11B illustrate a cross-sectional view of a protective
device and its equivalent electrical diagram in accordance with an
exemplary embodiment;

[0025] FIGS. 12A and 12B illustrate a cross-sectional view of an a
protective device with split thermal disconnectors and its equivalent
electrical diagram in accordance with an exemplary embodiment;

[0026] FIGS. 13A and 13B illustrate front and profile views of a
protective component to be housed in an inner volume of a cartridge in
accordance with an exemplary embodiment;

[0027] FIGS. 14A, 14B, 14C, 15A, 15B, and 16A illustrate different views
of a protective device with two protective components in accordance with
an exemplary embodiment;

[0028]FIG. 16B illustrates an equivalent electrical diagram of a
protective device with two protective components in accordance with an
exemplary embodiment;

[0029] FIGS. 17A and 17B illustrate a protective device with a protective
component having two non-linear blocks for a photovoltaic installation in
accordance with an exemplary embodiment.

DETAILED DESCRIPTION

[0030] An exemplary protective device is disclosed for protecting an
electrical installation from surges. The protective device comprises two
connection terminals for connecting the device to the electrical
installation to be protected, a protective component protecting against
overvoltages, where the protective component is electrically connected to
the two connection terminals. The protective device also includes a
thermal disconnector comprising a conductive contact blade maintained in
a first position in which the contact blade ensures an electrical
connection between the protective component and one of the two connection
terminals, where the thermal disconnector being provided to make the
contact blade go to a second position when the temperature of the
protective component exceeds a predetermined threshold in which second
position said electrical connection is open. The contact blade and said
one of the two connection terminals are part of a single and same piece.

[0031] According to an exemplary alternative, the protective component
protecting from overvoltages can be a varistor.

[0032] According to an exemplary alternative, the device can include a
member reducing or eliminating electric arcs forming during movement of
the contact blade from the first position towards the second position,
the reducing or eliminating member can be chosen from the group of arc
reducing or eliminating members comprising electric means, electronic
means, electromechanical means, and mechanical means.

[0033] According to an exemplary alternative, the piece to which the
contact blade and the one of the two connection terminals belong has an
IACS conductivity greater than or equal to for example 70%, preferably
greater than or equal to for example 90%, still more preferably greater
than or equal to for example 95%.

[0034] According to an exemplary alternative, the piece to which the
contact blade and said one of the two connection terminals belong can be
made from copper with a copper content greater than or equal to 99.9%.

[0035] According to an exemplary alternative, the piece formed by the
contact blade and the one of the two connection terminals can include a
flexible part intermediate between the contact blade and the terminal to
allow the contact blade to move relative to the terminal, between the
first position and the second position.

[0036] According to an exemplary alternative, the contact blade can be
elastically stressed towards the second position, the thermal
disconnector comprising a thermosensitive element in thermal contact with
the protective component, the thermosensitive element maintaining the
contact blade in the first position up to the predetermined temperature
threshold and releasing the contact blade when the temperature of the
protective component exceeds the predetermined threshold.

[0037] According to an exemplary alternative, the thermosensitive element
can be a thermofusible braze by which the contact blade is welded to a
pole of the protective component.

[0038] According to an exemplary alternative, the part of the contact
blade welded to the pole by the thermofusible braze can be connected to
the rest of the contact blade by a local restriction of the section of
the blade to concentrate the heat given off by the protective component
at the thermofusible braze.

[0039] According to an exemplary alternative, the contact blade can extend
primarily in a first plane parallel to one of the main faces of the
protective component, the movement of the contact blade between the first
position and the second position being done mainly in the first plane.

[0040] According to an exemplary alternative, the part of the contact
blade welded to the pole of the protective component can be tinned.

[0041] According to an exemplary alternative, the device can comprise a
second thermal disconnector to disconnect the protective component from
the electrical installation when the temperature of the protective
component exceeds a predetermined threshold.

[0042] The disclosure also relates to an exemplary device for protecting
an electrical installation from surges. The protective device can
comprise a component for protecting from overvoltages and two connection
terminals for connecting the device to the electrical installation to be
protected. The protective component is electrically connected to the two
connection terminals. The protective component can for example be a
varistor. It will be understood that this can be a block of several
varistors connected to each other serially or in parallel.

[0043] An exemplary device can also comprise a thermal disconnector
comprising a conductive contact blade. The conductive contact blade can
be kept in a first position, called the closed position, in which the
contact blade ensures an electrical connection between the protective
component and one of the two connection terminals. The thermal
disconnector is provided to make the contact blade go to a second
position, called the open position, when the temperature of the
protective component exceeds a predetermined threshold. When the contact
blade is in the second position, the electrical connection between the
protective component and the one of the two connection terminals is then
on.

[0044] Furthermore, the conductive contact blade and the one of the two
connection terminals can be part of a single and same (common) piece. In
the event of a failure of the protective component by short circuit, the
short circuit current supplied by the power grid under nominal voltage
then passes through the protective device and flows through said
single-unit piece comprising the connection terminal and the conductive
contact blade without encountering contact or weld electrical resistance.
This absence of contact or weld electrical resistance can limit the
heating of the piece when it is passed through by this short circuit
current, which can have a very high intensity. Limiting the heating of
the piece can contribute to limiting the risk of destruction thereof by
melting, which would be likely to cause the creation of uncontrolled
electric arcs able to cause a fire outbreak. The single-unit piece
comprising the connection terminal and the conductive contact blade can
thus contribute to maintaining the passage of the current through the
protective device reliably, at least for the time needed for outside
overvoltage protection to interrupt the current. The proposed overvoltage
protection device thereby can have improved resistance to short circuit
currents.

[0045]FIG. 1 illustrates a perspective view of a protective cartridge 20
of a low-voltage electrical installation in accordance with an exemplary
embodiment. The protective cartridge 20 comprises a protective device for
protection from over voltages. This protective cartridge 20 can be pinned
on a base 82, which can be mounted on a DIN rail with a standardized
electric board. Pinning the cartridge 20 on a base 82 facilitates a
connection of the protective device to the low-voltage electrical
installation to be protected. As provided herein, "low-voltage electrical
installation" refers to equipment with an assigned RMS voltage up to, for
example, 1,000 V in alternating current or up to, for example, 1,500 V in
direct current. The fastening on a DIN rail is standard for such
electrical installations. The described device for protecting from
overvoltages is also adapted to the protection of photovoltaic generator
installations.

[0046] The current use of cartridges and bases for a DIN rail, in the
low-voltage field, can impose a compact design constraint of the devices
for protecting from overvoltages.

[0047] FIGS. 2A, 2B illustrate front and profile views of a protective
cartridge in accordance with an exemplary embodiment.

[0048] FIGS. 2A and 2B respectively, illustrate one of the main faces of
the cartridge 20 and the edge of the cartridge 20. The cartridge 20,
which houses the protective device has outer dimensions A×B×C
smaller than or equal to 57×50.5×17.6 mm, for example.

[0049] FIGS. 3A and 3B illustrate the inner volume 21 defined by the case
of the cartridge 20 housing the protective device in accordance with an
exemplary embodiment. FIG. 3A shows a cross-section of the case along one
of the main faces of the case. FIG. 3B shows a cross-section of the case
along the edge of the case. The cartridge 20 intended to house the
protective device thus has a parallelepiped inner volume 21 having
dimensions C'×A'×B' smaller than or equal to
15×42×43 mm, for example.

[0050] Described below are various exemplary features, which enable the
protective device to have a compact structure, thereby allowing it to be
housed in the inner volume 21.

[0051]FIG. 4 illustrates a mobile contact of the protective device in the
closed position in accordance with an exemplary embodiment. As shown in
FIG. 4, the cartridge 20 houses the protective device, which includes a
varistor 30 as a protective component, and a conductive contact blade 44
that forms a mobile contact of a thermal disconnector. Alternatively, the
mobile contact can be formed by a braid or a wire or other suitable
structure as desired, to ensure the connection of the protective
component to the electrical installation. The protective device 30
includes two terminals 38 and 48 for connecting the device to the
electrical installation. The varistor 30 has two poles each connected to
a respective one of the terminals 38 and 48. FIG. 4 shows the protective
device with the contact blade 44 in the closed position. The contact
blade 44 is electrically connected to the pole 34 (visible in FIG. 5) of
the varistor 30. The pole 34 can thus constitute a fixed contact of the
thermal disconnector. The pole 34 is connected to the terminal 48 via the
contact blade 44. Moreover, the contact blade 44 is elastically stressed
by a torsion spring 50. The connection of the terminals 38 and 48 to the
electrical installation to be protected can be established, in this
example, via the base 82 previously described with reference to FIG. 1.
The terminals 38 and 48 can be implemented as male terminals, such as
pins or other suitable structure as desired.

[0052] FIGS. 5 and 6, illustrates a mobile contact of the protective
device in the open position and a diagram of the removed part of the case
in accordance with an exemplary embodiment. FIG. 5 shows the same
protective device with the contact blade 44 in the open position. The
contact blade 44 can be disconnected from the pole 34 of the varistor 30.
In this position, the pole 34 of the varistor 30 is no longer connected
to the terminal 48.

[0053] FIGS. 5 and 6 illustrate the cartridge 20 with the case 20 of the
cartridge open. The case is made up of an upper flange 23 shown in FIG. 6
and a lower flange 24 shown in FIG. 5. The compactness of the protective
device enables the formation of an "equipped cradle" with the lower
flange 24. FIG. 5 illustrates the contact blade 44 in the disconnected
state.

[0054] The thermosensitive element of the thermal disconnector can be a
thermofusible braze 70 via which the contact blade 44 is at the pole 34
of the varistor 30. This braze can be visible on the pole 34 of the
varistor 30 as shown in FIG. 5. The braze 70 ensures the electrical
connection between the blade 44 in the closed position and the terminal
34 until the protective component 30 reaches the threshold temperature
(for example 140° C.), which is indicative of a failure of the
varistor 30. When the varistor 30 reaches the threshold temperature, the
braze 70 melts and the end of the contact blade 44 that was connected to
the pole 34 of the varistor 30 moves away from the latter under the
action of the spring 50. As a result, the electrical connection between
the contact blade 44 and the pole 34 is broken.

[0055] In the exemplary embodiments of the present disclosure, the
protective device can face surge situations without a risk of explosion
or fire outbreak, at least if the protective device is likely to be
subjected to such surge conditions. For example, the exemplary
embodiments can be designed to satisfy the tests provided by the UL
standard, paragraph 39 or by the UTE guide, paragraph 6.7.4. To this end,
the disclosed exemplary embodiments provide fast thermal disconnection of
the varistor 30. In these surge situations, current passing through the
varistor increases gradually until the varistor goes into a steady-state
short-circuit.

[0056] The time the varistor 30 spends in short circuit can depend, for
example, on a ratio between the surge and the maximum operating voltage
allowable by the varistor and the electric behavior of the varistor
(e.g., variation of the resistivity of the varistor as a function of the
voltage applied to it). On one hand, when the ratio between the surge and
the maximum allowable voltage of the varistor 30 is high, the time spent
by the varistor 30 in short circuit is low. On the other hand, when the
behavior of the varistor is strongly non-linear (e.g., the resistivity of
the varistor varies very sharply with the increase of the voltage applied
to it), the time spent by the varistor 30 in short circuit is low. It is
then possible to choose the varistor as a function of these different
features to increase the time spent in steady-state short circuit under
the in use conditions of the varistor. The current surge phase can be
accompanied by an increase in the temperature of the varistor 30, during
the time spent by the varistor in short circuit. The exemplary thermal
disconnector can be designed to ensure a disconnection in the
transitional phase of the behavior of the varistor before the current
passing through it becomes too high to be able to be interrupted by the
thermal disconnector. This design involves a fast detection of the
increase in the temperature of the varistor.

[0057] Various technical characteristics of the exemplary embodiments of
the present disclosure contribute to obtaining this fast disconnection.

[0058] The pole 34 can be arranged on one of the main faces of the
protective component 30. Such a main face of the protective component is
shown by the cross-hatched area 32 in FIGS. 4 and 5.

[0059] FIG. 7 illustrates a front view of the varistor housed with the
rest of the protective device in the cartridge in accordance with an
exemplary embodiment. FIG. 7 shows a perspective view of the varistor 30
seen perpendicularly to the plane of its main face 32. The pole 34 can be
arranged inside a central area on the main face 32. This central area is
represented by an imaging circle 86 in broken lines in FIG. 7. The
central area can be situated inside the imaginary circle 86 centered on
said main face 82 of the block 80 and having a diameter equal to 75%, for
example, of the diameter of the circle drawn on the main face 82 of the
block 80. The arrangement of the pole 34 on the main face 32 in the
central area can ensure fast detection, by the thermofusible braze 70, of
the increase in the temperature of the varistor 30 during the
transitional phase where the current passing through it increases. The
runaway of the varistor 30 can cause an increase in the temperature first
in the deteriorated zones of the varistor 30. These deteriorated zones
correspond to zones of the varistor 30 having uncontrolled design flaws.
The location of these zones is not known a priori, such that the thermal
runaway of the varistor starts in an undetermined area. The arrangement
of the pole 34 in the central area can establish that the pole 34 is
statistically closest to the area where the thermal runaway of the
varistor begins.

[0060] The pole 34 of the varistor 30 can advantageously extend along the
main face 32, and not protrude perpendicular thereto. As a result, the
braze 70 is done on the pole 34 at a brazing surface that is parallel to
the main face 32 of the varistor 30. The braze 70 has its thickness in a
direction perpendicular to the main face of the protective component. As
a result, the entire braze 70 is as close as possible to the varistor 30
and can establish immediate communication with it regarding the
temperature of the varistor 30. This measure can be advantageous relative
to known solutions in which the pole of the protective component forming
the fixed contact of the thermal disconnector extends in a plane
perpendicular to the main face of the protective component. The braze can
extend along the perpendicular plane and part of the braze can be kept at
a distance from the protective component. When the protective component
fails, the braze is first stressed thermally in a portion closest to the
protective component. The delay of a temperature increase of the varistor
arriving at the portion of the braze that is farthest from the protective
component 30, which can slow the thermal disconnection.

[0061] Moreover, the speed of thermal disconnection can also be improved
by the exemplary varistor 30 of the present disclosure, through the
electrode forming the pole of the varistor, which serves to transmit the
heat given off by the varistor to the thermosensitive element of the
thermal disconnector.

[0062] Thus, the electrode of the varistor can be formed by a conducting
plate 84, as shown in FIG. 7. The varistor 30 can also include a block
80. The block 80 has an electrical resistance which varies as a function
of the voltage applied to the block 80. This block 80 can establish the
active part of the varistor 30 and can be used to limit the overvoltages
by having a low resistance for overvoltages with high amplitudes like
those occurring during lightning. The conducting plate 84 can be arranged
on a main face 82 of the block 80. The main faces of the block 80
correspond to the main faces of the varistor 30. The plate 84 has a
protruding part forming one of the connection poles 34 of the varistor.
Similarly, a second pole 36 of the varistor 30 can be formed by a
protruding part of a conducting plate arranged on another main face of
the block 80 of the varistor 30.

[0063] The varistor 30 can include an electrically insulating coating
applied on the assembly formed by the main face 82 of the block 80 and
the plate 84. Thus, the assembly formed by the main face 82 of the block
80 and the plate 84 can be electrically insulated from its surrounding
environment, including the mobile contact of the protective device. In an
exemplary embodiment, the assembly formed by the block 80 and the plate
84 can be completely coated with the electrically insulating coating
through which the different connection poles of the varistor also emerge
to produce an electrical connection with the rest of the protective
device, for example, with the contact blade 44.

[0064] The protruding part forming the pole 34 can emerge outside the
electrically insulating coating to allow an improvement of the
interrupting capacity as described below.

[0065] The protruding part forming the pole 34 can be connected to the
rest of the plate 84 on at least half of its perimeter to improve the
speed of the disconnection. During the deterioration of the varistor 30
subjected to surges, the leakage current of the varistor 30 increases
until the varistor 30 goes into steady-state short circuit. This
transitional phase for increase of the leakage current is accompanied by
an increase in the temperature of the varistor 30. This temperature
increase can be gradual. The temperature first increases in the core of
the block 80 of the varistor 30 in areas having homogeneity flaws. The
temperature increase can spread by conduction in the entire block 80 of
the varistor up to the outer faces of the block for example, up to the
main face 82 of the block 80. The arrangement of the conducting plate 84
on the main face 82 of the block 80 can allow a minimum propagation time
of the temperature increase from the defective areas of the block 80 up
to the plate 84 forming the electrode of the varistor 30. The plate 84
has an electrically conductive characteristic, allowing the plate to form
an electrode. The plate 84 also has a thermally conductive characteristic
to ensure a rapid propagation of the temperature increase to the pole 34
of the varistor 30 after the temperature increase has reached the plate
34. The conducting plate can be made of copper. The connection of the
protruding part forming the pole 34 to the rest of the plate 84 over at
least half of the perimeter of the pole 34 ensures effective thermal
conduction from the plate 84 towards the pole 34, despite the location of
the areas of the block 80 having defects relative to the pole 34. Over
time, a decrease in the reaction time of the varistor can be observed.
This is the time that elapses between the first deteriorations of areas
of the block 80 of the varistor and the temperature increase of the pole
34 of the varistor 30.

[0066] FIGS. 8A, 8B, and 8C each illustrate a perspective view of an
electrode of the varistor in accordance with an exemplary embodiment.
FIG. 8A illustrates one exemplary embodiment of the part forming the pole
34. This part forming the pole 34 can be connected to the rest of the
plate 84 on its sides with dimensions D. The sides with dimensions E of
the part forming the pole 34 have been cut out of the plate 84 and then
do not participate in the thermal conduction.

[0067]FIG. 8B illustrates another exemplary embodiment of the part
forming the pole 34. In this embodiment, the part forming the pole 34 can
be arranged on the edge of the plate 84.

[0068] All of these embodiments forming the pole 34 have a connection with
the rest of the plate over at least half of the perimeter of the pole 34.

[0069] For example, the part of the plate forming the connection pole can
be connected to the rest of the plate 84 over at least 80%, for example,
of its perimeter to ensure better thermal conduction.

[0070] In another example, the part forming the pole 34 can be connected
to the rest of the plate 84 over its entire perimeter, as illustrated in
FIG. 8C. The heat, due to the temperature increase of the block 80 and
picked up by the plate 84, can then be thermally conducted to the pole 34
over its entire perimeter. The thermal transfer and the speed of the
disconnection can thereby be improved.

[0071] All of these embodiments of the part forming the pole 34 were
obtained by drawing of the plate 84. Drawing is a manufacturing technique
to obtain, from a planar and thin sheet of metal, an object whereof the
shape cannot be developed. In the embodiment of FIG. 8A, the plate 84 has
been cut out beforehand to facilitate the deformation of the plate 84.

[0072] The formation of one of the poles of the varistor by drawing the
plate 84 can establish continuity between the part of the plate arranged
on the main face 82 of the block 80 and the drawn part.

[0073] The part of the plate 84 forming the pole 34 of the plate 84 can
also be arranged at the central zone of the block 80 that corresponds to
the central zone delimited by the imaginary circle 86 drawn in FIG. 7,
which allows a fast speed of disconnection as previously demonstrated.
With a similar result, in an exemplary embodiment the conducting plate 84
can be centered on said main face 82 of the block 80.

[0074] The rest of the conducting plate 84 around the protruding part
forming the pole 34 can be solid. The rest of the plate 84 then does not
have any material recess or hole inside the surface delimited by its
outer perimeter. By not having holes, the plate 84 can have a significant
surface for picking up the temperature increase of the block 80 to
improve the speed of the thermal disconnection. With the same aim, the
surface of the plate 84 can be arranged to be in contact with the main
face 82 of the block 80 to have an area that is at least half the area of
the main face 82 of the block 80.

[0075] In an exemplary embodiment, the plate 84 can have a thickness
smaller than or equal to 0.7 mm so as to limit the amount of material to
be heated before the temperature increase reaches the pole 34. The plate
84 can preferably have a thickness greater than or equal to 0.3 mm, for
example, to allow the plate to withstand the mechanical stresses as
described in the present disclosure.

[0076] Another measure comprises (e.g., consists of) choosing, for the
thermofusible braze 70, an alloy with a low melting temperature to
establish a quick disconnection of the contact blade 44. A low melting
temperature of the braze 70 can be used to quickly obtain a covering of
the thermal disconnector. In an exemplary embodiment, the tin/indium
alloy In52Sn18 can be used because it has a liquidus temperature at
118° C. while the alloys traditionally used have a liquidus
temperature generally greater than 130° C. Moreover, this alloy
complies with European directive 2002/95/CE, called RoHS (Restriction of
the use of certain Hazardous Substances in electrical and electronic
equipment).

[0077] Still another measure comprises (e.g., consists of) optimizing the
shape of the connecting blade 44. FIGS. 9 and 10, illustrate a profile
and perspective view of an electrical contact piece in accordance with an
exemplary embodiment. For example, FIGS. 9 and 10 illustrate, in profile
and perspective, respectively, an exemplary embodiment of the connecting
blade 44 of FIG. 5. The contact blade 44 has a part 42 that can be welded
to the pole 34 by the braze 70. The part 42 can be connected to the rest
of the contact blade 44 by a local restriction 58 of the section of the
contact blade 44. This restriction 58 of the contact blade 44 can allow
the concentration of heat released by the protective component 30 at the
part 42--and therefore at the braze 70--because the diffusion of the heat
from the part 42 towards the rest of the contact blade 44 is limited by
the local restriction 58. As a result, the temperature increase of the
braze 70 is faster during the temperature increase of the varistor 30.
The speed of the opening of the thermal disconnector can then be
increased.

[0078] The surface of the part 42 can correspond to the section of the
braze 70. The section of the braze 70 can be chosen as a function of the
mechanical considerations described below.

[0079] The part 42, as well as the braze 70, can have a disc shape to
allow better homogeneity of the heating of the braze 70. The part 42 can
thus have an average diameter of this disc. In an exemplary embodiment,
the local restriction 58 can have a length smaller than 80% of the
average diameter of the part 42 to establish a sensitive concentration
effect on the braze 70 of the heat given off by the varistor 30. In
another exemplary embodiment, the local restriction can have a length
smaller than 70% of the average diameter of the part 42. The length of
the aforementioned local restriction 58 can extend by the shortest
distance separating two opposite edges of a main face of the contact
blade 44: this length is referenced `L` in FIG. 9.

[0080] The local restriction 58 can be arranged near the braze 70 to limit
the losses of thermal energy between the local restriction 58 and the
braze 70. The distance from the local restriction 58 to the braze 70 can
be estimated by the ratio between the surface of the braze 70 (e.g. the
section of the braze previously described) and the surface of the part 42
(shown by cross-hatching and to the right of the restriction 58 on FIG.
9). In an exemplary embodiment the ratio can be greater than 70%, and in
another exemplary embodiment is preferably greater than, for example,
80%.

[0081] The exemplary characteristics previously described each can
contribute to increasing the speed of the thermal disconnection, can be
implemented independently of each other, in any suitable combination
depending on the desired disconnection speed. These measures can be used
to meet the specification of the UL standard paragraph 39 and/or of the
UTE guide paragraph 6.7.4. Combining all of these measures can be used to
meet the particularly strict specifications of the UL standard, paragraph
39.

[0082] In an exemplary embodiment, the protective device can be designed
to have an improved interruption capacity. The improved interruption
capacity can be useful both in the case of a thermal disconnection under
nominal operating voltage and in the case of a surge such as in the tests
of UL standard paragraph 39 and/or the UTE guide paragraph 6.7.4.

[0083] Different technical characteristics can contribute to obtaining an
improved interrupting capacity.

[0084] Thus, the protective device can comprise a member for reducing or
eliminating arcs forming during the movement of the contact blade 44
towards the open position. Such an arc reduction or elimination member
can be useful for electrical installations powered with direct current.
Such members are for example made up of electrical means (such as a
capacitor 22), electronic means, electromechanical means (such as an arc
extinction chamber), or mechanical means (such as an insulating flap
inserted between the mobile contact and the fixed contact, by elastic
stress or by gravity). When the capacitor 22 is used, it can be
positioned parallel to the thermal disconnector to reduce the voltage of
the electric arc forming during the movement of the contact blade 44
towards its open position. In this sense, FIGS. 11A and 11B, illustrate a
cross-sectional view of a protective device and its equivalent electrical
diagram in accordance with an exemplary embodiment. FIG. 11B shows the
electrical diagram corresponding to the protective device of FIG. 11A,
which shows it diagrammatically in transverse cross-section.

[0085] FIGS. 12A and 12B illustrate a cross-sectional view of a protective
device with split thermal disconnectors and its equivalent electrical
diagram in accordance with an exemplary embodiment. For the installations
powered with direct current or those powered with alternating current,
the protective device can include a second thermal disconnector as shown
in FIGS. 12A and 12B. The second disconnector can be formed by a mobile
contact 64 and a fixed contact 36 on the same varistor 30. The fixed
contact 36 corresponds in FIG. 12A to the second pole of the varistor 30.
The mobile contact 64 can be made by a contact blade similarly to the
contact blade 44 of the first thermal disconnector. The presence of the
second thermal disconnector on the same varistor can increase the
interruption capacity of the proposed protective device, given that the
clearances between mobile contact and fixed contact(s) of the two thermal
disconnectors are added. As shown in FIG. 12B, which shows the equivalent
electrical diagram of the protective device of FIG. 12A, it can be
possible to have capacitors 22 in parallel with each of the thermal
disconnectors to further improve the interruption capacity.

[0086] Moreover, as illustrated in FIG. 5, the protective device can
include a torsion spring 50 to elastically stress the contact blade 44
from the closed position to the open position. In such an embodiment,
when the varistor 30 reaches the threshold temperature, the braze 70
melts and releases the contact blade 44, which is driven towards the open
position due to the elastic stress by the spring 50. The use of a spring
50 separate from the contact blade 44 can allow calibration of the
opening speed of the contact blade 44 and precise orientation of the
stress force of the contact blade 44. In traditional systems, the contact
blades forming the mobile contact of a thermal disconnector can be
elastically stressed due to the intrinsic elasticity of the contact
blades. The elasticity can be intrinsically related to the contact blade,
it is then difficult to provide a significant opening speed of the
contact blade without modifying the geometry of the contact blade. In an
exemplary embodiment of the present disclosure, the spring 50 can be
dimensioned to drive the contact blade 44 towards the open position with
a significant opening speed without altering the geometry of the contact
blade 44. The contact blade 44 can then be defined solely as a function
of other considerations. Moreover, the choice of a high opening speed of
the thermal disconnector can be used to increase the interruption
capacity of the disconnector.

[0087] As illustrated in FIGS. 9 and 10, the contact blade 44 comprises a
support 56 for the spring 50, which can transmit the stress from the
spring 50 to the contact blade 44. As shown in FIGS. 4 and 5, the contact
blade 44 extends in a first plane parallel to the main face 32 of the
varistor 30 with a movement of the contact blade 44 between the closed
position and the open position being done mainly in this first plane.
With reference to FIG. 5, it is thus possible to obtain a substantial
clearance D between the mobile contact (e.g. the contact blade 44) and
the fixed contact--(e.g. the pole 34) of the thermal disconnector. Thus,
the clearance (e.g., insulation distance) for a thermal disconnector can
be substantially greater than 5 mm, for example, and reach at least, for
example, 10 mm.

[0088] Moreover, such a movement of the contact blade 44 in a plane
parallel to the main face 32 can also allow obtaining a compact
protective device that can be housed in the cartridge 20. In traditional
solutions of thermal disconnectors formed by a disconnection contact
blade, the movement of the contact blade towards the open position can be
a movement in a direction perpendicularly to the main face of the
protective component. In such devices, the increase of the disconnection
distance goes through the increase of the thickness of the device (i.e.
the dimension of the device in the direction perpendicular to a main face
of the protective component), which damages its compactness.

[0089] The movement of the contact blade 44 parallel to the main face 32
of the varistor 30 can be confined in a volume having for base the main
face 32 of the varistor and having a small thickness relative to the
dimensions of the varistor. Such a movement of the blade 44 along the
main face 32 of the varistor 30, and therefore having larger dimensions
than the varistor 30, causes the possibility of obtaining a substantial
interruption distance inside the volume confining the movement of the
contact blade 44. The thickness of this volume being small, the
compactness of the protective device can be close to the compactness of
the varistor 30. This embodiment of the contact blade 44 can be
particularly advantageous when the protective device comprises a second
thermal disconnector on the same varistor as previously described. A
compact design is then obtained according to FIG. 12A.

[0090] With reference to FIG. 8D and as previously described, the
electrode 84 of the varistor 30 can have the protruding part forming the
pole 34. This part forming the pole 34 emerges outside the electrically
insulating coating such that the brazing surface for the electrical
connection of the pole and drawn portion extends above the level of the
electrically insulating coating, as shown by FIG. 12A.

[0091] The arrangement of the part of the plate 84 forming the pole 34
protruding and emerging from the electrically insulating coating ensures
that the contact blade 44, forming the mobile contact, performs a
movement towards the open position, in a manner parallel to the main face
32 of the varistor 30 while remaining at a distance from the insulating
coating. The movement towards the open position is thus done without
friction of the contact blade 44 on the insulating coating. The absence
of friction of the contact blade 44 on the insulating coating can obtain
a good disconnection speed without dragging liquefied residue from the
braze 70 on the main face 32 of the varistor 30. In one example, a good
disconnection speed of the thermal disconnector can contribute to
improving the interruption capacity of the disconnector. In another
example, preventing the formation of a trail of liquefied braze 70 can
establish that the clearance procured by the thermal disconnector in the
on state is indeed equal to the distance separating the contact blade 44
and the pole 34, thereby improving the interruption capacity.

[0092] The arrangement of the part of the plate 84 protruding to form the
pole 34 can also electrically insulate the blade 44 from the electrically
insulating coating without using an additional separating partition. The
protective device can thus be made such that only an air blade separates
the main face 32 from the contact blade 44 during its movement from the
closed position towards the open position. The absence of an additional
separating partition between the contact blade 44 and the main face 32 of
the varistor 30 can further reduce the bulk of the protective device.

[0093] With the same aim of improving the interruption capacity, the part
forming the pole 34 can have its braze surface at least 0.1 mm above the
level of the electrically insulating coating. In an exemplary embodiment,
the braze surface can be preferably situated at least, for example, 0.3
mm from the level of the electrically insulating coating.

[0094] In an exemplary embodiment, the electrically insulating coating can
have a thickness between 0.1 mm and 1 mm. In another exemplary preferred
embodiment, the thickness is greater than or equal to 0.6 mm to allow an
improved electrical insulation of the varistor 30 relative to the rest of
the protective device.

[0095] The previously described characteristics each contribute to
increasing the interruption capacity. They can be implemented
independently of each other, and in any combination depending on the
desired interruption capacity.

[0096] The protective device can be designed to reliably withstand shock
currents, for example, to pass the tests in standards IEC paragraph 7.6
or UL paragraph 37, or the UTE guide paragraph 6.6 depending on the case.

[0097] The production of the braze 70 in the plane of the main face 32 of
the varistor 30 already described can withstand the electrodynamic
stresses due to the lightning strike. The resistance of the braze 70 to
the mechanical pulling out of electrodynamic forces can be adapted by
increasing the section of the braze 70, for example, by increasing the
surface of the braze 70 welded to the pole 34--(e.g., by increasing the
brazing surface of the part forming the pole 34). In known solutions, the
section of the brazing extends in a plane perpendicular to the main face
of the protective component. The dimensioning of the section of the braze
relative to the electrodynamic forces can cause an increase in the
thickness of the entire protective device (i.e. in the direction
perpendicular to the main face of the protective component). In the
protective device proposed with the braze 70 made in the plane of the
face 32 at the pole 34 arranged on the face 32, the increase in the
section of the braze 70 is done along the plane of the face 32. The
increase of the section of the braze 70 for resisting electrodynamic
forces is not limited by the compactness requirement of the protective
device. As a result, a section of the braze 70 that is larger than or
equal to 50 mm2, for example, or even larger than or equal to 100 mm2,
for example, can be obtained without affecting the compactness of the
protective device to be housed in the cartridge 20 as previously
described. Even for surfaces with a fairly substantial weld section, the
speed of the disconnection can be satisfied with the different
characteristics already described.

[0098] With reference to FIG. 9, the contact blade 44 can be secured to a
flexible part 46. This flexible part 46 can form a bend 46 (or a lyre)
around an axis perpendicular to the plane of FIG. 9. This bend 46 allows
the contact blade 44 to move between the open position and the closed
position. In case of shock currents passing through the protective
device, the electrodynamic stresses stress the flexible bend 46 towards
the open position. Such a stress towards the open position of the bend 46
can cause a stress of the contact blade 44 towards the open position. In
other words, the electrodynamic forces can exert shearing stresses on the
braze 70. However, as previously described, the braze 70 can be
dimensioned to withstand stresses such as shearing without damaging the
compactness of the device. The flexible bend 46 therefore can contribute
both to the compactness of the protective device and its resistance to
shock currents.

[0099] The shearing stress of the braze 70 can eliminate problems
encountered during a traction stress of the braze. Indeed, in a situation
involving traction of the braze, the strains in the braze may not be
uniformly distributed. The part of the braze with the strongest strains
can deteriorate locally, creating a start of the braze that decreases the
effective section of the braze faced with the traction. There is then a
cleavage situation where the most stressed part of the braze can
gradually cause the entire braze to be pulled out. The shearing stress of
the proposed braze allows a more uniform distribution of the strains in
the braze 70, avoiding a situation equivalent to traction cleavage.

[0100] In an exemplary embodiment the material of the bend 46 can have a
low elastic resistance (Re). A low elastic resistance allows the bend 46
to absorb part of the energy by opening in a plastic manner. The
absorption of part of the energy due to the electrodynamic effects can
limit the stress of the braze 70. The elastic resistance can be
approached by the plastic deformation strain at 0.2% (noted Rp0.2). When
the material used for the bend is copper Cu-al as discussed in more
detail below, the latter has an Rp0.2 that is low, e.g., 250 MPa
(Nmm-2)).

[0101] The use of the tin/indium alloy In52Sn18 for the braze 70 can
obtain a shearing resistance in the vicinity of 11.2 MPa (Nmm-2), which
constitutes a good resistance compared to the alloys traditionally used
for the braze. A known alloy such as Bi58Sn42 has a shearing resistance
in the vicinity of only 3.4 MPa. As a result, the material contribution
for the production of the braze 70 can be limited by decreasing the
section of the braze 70 for example to an area of 25 mm2 while having a
satisfactory mechanical shearing resistance.

[0102] As illustrated by FIGS. 9 and 10, the contact blade 44 can comprise
a stiffening zone 52 of the piece 40. The bending inertia of the contact
blade 44 can be increased so that the disconnection stress of the contact
blade 44 by the spring 50 or by the electrodynamic forces is
quasi-exclusively a pure shearing. The dimensioning of the braze 70 for
resistance to shock currents can be facilitated. However, a low bending
inertia can be provided between the part 42 of the contact blade 44 that
is welded to the pole 34 and the restriction 58. This allows the
dimensional play during assembly of the different pieces of the
protective device without having to deform the contact blade 44 to weld
it to the pole 34.

[0103] In an exemplary embodiment, the part 42 of the contact blade 44,
intended to be welded to the pole 34 by the braze 70, can be tinned. The
tinning of the part 42 can improve the quality of the braze causing
better mechanical resistance thereof, for example, to the shock currents.

[0104] The exemplary characteristics previously described each contribute
to increasing the mechanical resistance to shock currents while allowing
a compact implementation of the protective device. They can be
implemented independently of each other, and in any suitable combination
depending on the desired mechanical resistance.

[0105] Due to the compactness, a varistor 30 with larger dimensions can be
housed within cartridges having the dimensions mentioned relative to
FIGS. 2A, 2B, 3A and 3B. For example, the varistor 30 can have a larger
thickness, which allows a higher operating voltage of the varistor. In
other words, the protective device can be adapted for an installation
operating under a higher voltage, (e.g., between 500 and 1000 V in the
case of photovoltaic generator installations), compared to the known 230
V or 400 V for alternating supply grids in Europe, for example.

[0106] FIGS. 13A and 13B illustrate front and profile views of a
protective component to be housed in an inner volume of a cartridge in
accordance with an exemplary embodiment. FIGS. 13A and 13B illustrate,
the dimensions A'', B'', C'' of a varistor 30 capable of being housed in
the cartridge 20 with the rest of the proposed compact protective device.
The dimensions A'' and B'' of the varistor 30 can be equal to 35 mm. The
varistor 30 can have a thickness C'' of up to 9 mm. The varistor 30 with
a thickness of 9 mm can have an exemplary operating voltage in the
vicinity of 680 V and has a leakage current in the vicinity of, for
example, 1 mA under a voltage of 1100 V in direct current. The
compactness of the protective device allows use of a voltage range of for
example, 75 V to 680 V, and allows the use of the protective device to
protect photovoltaic generator installations.

[0107] According to an exemplary embodiment, as shown in FIG. 12A, the
protective device having a dual thermal disconnector, the two poles 34
and 36 of the varistor 30 can be arranged on the main faces opposite the
varistor 30. The first electrical disconnector, which comprises the
contact blade 44 connected by thermofusible braze to the first pole 34 of
the varistor 30, is made as previously described. The second thermal
disconnector can comprise a contact blade 64 forming a mobile contact
connected by thermofusible braze to the second pole 36 of the varistor
30. This second disconnector can have the same exemplary characteristics
as the first disconnector, as described above.

[0108] In an exemplary embodiment, the protective device can be designed
to resist, in complete safety, the varistor 30 experiencing a short
circuit under nominal operating voltage for the time that specific short
circuit protection--such as a fuse or circuit-breaker outside the
device--intervenes. For example, it is provided to be able to satisfy
standard IEC paragraph 7.7.3. The difficulty comes from the fact that
this external protection has a certain reaction time during which high
currents pass through the protective device. The protective device should
not explode or trigger a fire during that time.

[0109] To achieve this objective, the conductive pieces of the protective
device are limited, for example, in its thermal disconnector. Indeed, the
short circuit current can cause heating of these pieces by the Joule
effect. Uncontrolled heating of the different pieces of the protective
device can lead to the melting of one of the pieces, constituting a
possible fire outbreak before the external devices cut the current.

[0110] Different characteristics contribute to limiting the heating of the
pieces of the protective device.

[0111] Thus, as illustrated by FIGS. 5, 9 and 10, the contact blade 44 and
the terminal 48 are part of a single and same piece to form the piece 40.
The piece 40 can be obtained by drawing, bending, or folding a laminated
sheet. Because the piece 40 is not obtained by assembling several pieces,
but only constitutes a single piece, the current passing through the
piece 40 from the terminal 48 to the contact blade 44 does not encounter
contact or weld electrical resistance. This absence of contact or weld
electrical resistance limits the heating of the piece 40 when it is
passed through by high intensity currents.

[0112] In an exemplary embodiment, the piece 40 can be made of copper with
a sufficient purity to have an IACS (international annealed copper
standard) conductivity greater than 70%. The IACS conductivity of a piece
corresponds to the ratio between a resistivity of 1.7241 μΩcm
and the resistivity of the piece, the IACS conductivity does not have
dimensions. As a result, the piece 40 has a low electrical resistivity
and therefore can establish the passage of the electrical current while
limiting its heating. From this perspective, it can be advantageous for
the purity of the copper to be such that its IACS conductivity is greater
than or equal to 90%, or even 95%, for example. In another exemplary
embodiment, copper such as Cu-al (or Cu-ETP are electrolyte copper),
having a purity of 99.9%, and an IACS conductivity of 100% can be used.
The electrical resistivity of the piece 40 can be less than or equal to
1.7241 μΩcm, for example, and limit the heating of the piece 40
subject to short circuit currents. In known solutions, contact blades
were used with an intrinsic elasticity to form the mobile contact of the
thermal disconnector. However, while copper alloys procure a sufficient
intrinsic elasticity, this elasticity is to the detriment of the
resistivity, which is substantially higher. In an exemplary embodiment,
the protective device, uses an elastic stress outside the contact blade
44 (by the spring 50 in our example) to produce a contact blade 44 with
copper having a sufficient purity to substantially limit its heating
during short circuit tests.

[0113] In an exemplary embodiment, the piece 40 can have a minimal section
provided to allow the continuous passage, without deterioration, of a
short circuit current to which the protective device can be exposed.
Moreover, in another exemplary embodiment, the piece 40 can have a
thickness of 0.4 mm to 0.6 mm, for example, to provide the flexibility of
the bend 46 discussed above. The thickness of the sheet used to obtain
the piece 40 can be equal to 0.5 mm.

[0114] Moreover, the contact blade 44 can have, outside the part 42, a
substantial heat exchange area with the ambient air, but without
compromising the compactness of the device. Thus, the main faces of the
contact blade 44 can extend parallel to the main face 32 of the varistor
30. The contact blade 44 thereby acts as a cooling fin, which further
improves the resistance of the piece 40 to short circuit currents.

[0115] The piece 40 can include zones with a maximum section to dissipate
the heat obtained by the Joule effect with a substantially constant
thickness, which can increase the contact surface of the piece 40 with
the ambient air and limit the heating during the passage of the short
circuit current. The maximum section of the piece 40 can be provided at
the contact blade 44, between the bend 46 on one hand and the part 42 on
the other, or if applicable the constriction 58.

[0116] An increase in the width of the piece 40 can also be provided
between the bend 46 and the terminal 48. FIGS. 9 and 10 illustrate a
cooling fin 54. This cooling fin 54, for example, can limit the
temperature elevation of the flexible bend 46 during the passage of the
short circuit current. The bend 46 can in fact have a minimal section of
the piece 40 for shaping considerations of the piece 40, or for
sufficient flexibility considerations of the bend 46.

[0117] The fact that the contact blade 44 can be provided with an exchange
surface limiting the heating of the piece 40 can locally decrease the
minimum section of the piece 40 previously mentioned, given the temporary
nature of the short circuit. It is thus possible to produce the
restriction 58 with a length smaller than or equal to 5.5 mm, or even 5
mm, for example, while staying, at that location, below the minimum
section of the piece 40 as previously defined.

[0118] In an exemplary embodiment, the material of the piece 40 can be
bare at the broaching 48 to limit the weld effect with the elastic
couplings of the base 82 through which the protective device is
electrically connected to the electrical installation to be protected.

[0119] The exemplary characteristics described above can each contribute
to increasing the resistance to short circuit currents, for example, as
verified by standard IEC paragraph 7.7.3. These characteristics can be
implemented independently of each other, and in any suitable combination
depending on the significance of the short circuit currents likely to be
provided by the supply grid of the installation to be protected.

[0120] According to an exemplary embodiment, two protective components can
be provided in the same cartridge 20.

[0121] FIGS. 14A, 14B, 14C, 15A, 15B, and 16A illustrate different views
of a protective device with two protective components in accordance with
an exemplary embodiment. FIGS. 14A and 14B show the protective device
comprising two varistors 30 each with a respective thermal disconnector
comprising a contact blade 44a connected to the pole 34 of the
corresponding varistor. FIG. 14A shows the protective device with the two
thermal disconnectors in the closed position. FIG. 14B shows the
protective device with the two thermal disconnectors in the open
position. FIG. 14C shows, diagrammatically in transverse cross-section,
one such embodiment of the protective device. The contact blades 44a can
each be welded to one of the varistors 30 at one of their main faces. The
other main faces of the varistors can be connected to each other so as to
produce a serial assembly of the varistors 30.

[0122] FIGS. 15A and 15B show an alternative embodiment of the protective
device comprising two varistors 30 each with a respective thermal
disconnector formed by a contact blade 44b connected to the pole 34 of
the corresponding varistor. FIG. 15A shows the protective device with the
two thermal disconnectors in the closed position. FIG. 15B shows the
protective device with the two thermal disconnectors in the open
position.

[0123] In the embodiments of FIGS. 14A, 14B, 14C, 15A and 15B, the
varistors 30 can be arranged next to each other in a same plane parallel
to the main faces of the varistors. With reference to FIG. 14C, the
thickness of each varistor 30 can be similar to the thickness of the
varistor 30 in the exemplary embodiments of the protective device with a
single varistor. The operating voltage of the protective device can then
stay the same.

[0124] The production of each thermal disconnector in these embodiments
with two protective components can be in accordance with the preceding
description. The contact blades 44a or 44b can be made in a manner
similar to the preceding description. With reference to FIGS. 14A to 14C,
in an exemplary embodiment, the contact blades 44a and the terminal 48
can be part of a single and same piece 40a so as to procure resistance to
short circuit currents as previously described. With reference to FIGS.
15A and 15B, the contact blades 44b and the terminal 48 can be part of a
single and same piece to procure resistance to the short circuit currents
as previously described. In an exemplary embodiment of FIGS. 14A and 14B,
the contact blades 44 can be elastically stressed by a single torsion
spring 50a, whereas in the exemplary embodiment of FIGS. 15A and 15B, the
contact blades 44 can be elastically stressed by a respective torsion
spring made with a single wire 50b. The other numerical references of
FIGS. 14A, 14B, 14C, 15A and 15B are the same as those used for the
embodiments previously described.

[0125]FIG. 16A shows another alternative embodiment of the protective
device comprising two varistors 30 each with a thermal disconnector
formed by a respective contact blade 44 connected to a pole 34 of the
respective varistor. In this exemplary embodiment, the varistors 30 can
be arranged one above the other in the direction of the thickness of the
cartridge 20. The compactness imparted by the previously described
characteristics of the thermal disconnector produces an embodiment with
unique operating voltages for the varistors 30.

[0126] In these embodiments with two protective components 30 illustrated
in FIGS. 14A, 14B, 15A, 15B and 16A, the protective device can have an
electrical diagram in accordance with the one shown in FIG. 16B.

[0127] As illustrated in FIG. 16B, a capacitor 22 can be arranged in
parallel with two thermal disconnectors to improve the interruption
capacity, for example, during use in direct current.

[0128] The presence of this additional varistor in the same inner volume
21 of the cartridge 20 can establish the continuity of service and
protection when one of the varistors, having reached the end of its life,
has been disconnected. The disconnection of one of the varistors by a
thermal disconnector can be indicated to the user of the electrical
installation via a viewing element known in itself. The user is notified
that one of the protective components of the cartridge 20 has reached the
end of its life, with a function protecting against overvoltages still
being ensured by the second varistor for the time it takes the user to
replace the cartridge 20. FIG. 5 illustrates an exemplary embodiment of
the element 26 for viewing the status of one of the thermal
disconnectors.

[0129] Owing to the compactness of the thermal disconnector previously
described, the protective devices of FIGS. 14A, 14B, 15A, 15B and 16A,
16B can be in a cartridge 20 with dimensions as defined above.

[0130] According to an exemplary embodiment, the thermal disconnector can
be provided to include a plurality of varistors in the same protective
component. These varistors can be connected serially and/or in parallel
to each other depending on the applications. The varistors can then be
assembled in a compact mass that comprises at least two varistors.

[0131] FIGS. 17A and 17B illustrate a protective device with a protective
component having two non-linear blocks for a photovoltaic installation in
accordance with an exemplary embodiment. FIG. 17B illustrates one such
alternative embodiment of the protective component 30 made up of two
blocks 80 having a non-linear electrical resistance. These two blocks 80
form two varistors. The protective component 30 can include an electrode
98 forming a shared pole of the varistors to electrically connect the two
varistors to each other. The electrode 98 can connect a pole of the first
block 30 to a pole of the second block 30. The other poles 34 of the
blocks 80 can be connected to mobile contacts 44 of the thermal
disconnectors electrically connected to the terminals 38 and 48 of the
protective device as previously described. The set of varistors--e.g.,
the association of the two blocks 80--can be completely coated by the
electrically insulating coating 88 through which the connection poles of
the varistors, including the electrode 98, emerge. Such an embodiment of
the protective component can achieve the serial association of two
varistors with an intermediate potential connection via the electrode 98.

[0132] This exemplary embodiment of the protective component can be useful
for protecting photovoltaic installations. FIG. 17A illustrates a
photovoltaic installation comprising a photovoltaic panel 90. This panel
90 generates electrical voltage between the wires 95 and 96. A branch of
the wires 95 and 96 (not shown) can recover the electrical current
generated by the photovoltaic installation. To establish the protection
of said installation from overvoltages, each of the wires 95 and 96 can
be connected to one of the terminals 48 and 38 of the protective device
comprising the above-described protective component 30. The electrode 98
of the protective component 30 is grounded 94 via a spark gap 92. Each of
the wires 95 and 96 is thus grounded can be via a respective varistor and
a shared spark gap 92.

[0133] Other exemplary embodiments of the protective component 30 can
include associating a larger number of varistors serially or in parallel.
One embodiment of the protective component 30 can include (e.g., consist
of) superimposing several blocks 80 having a non-linear electrical
resistance by connecting the blocks 80 via electrodes 98 in a manner
similar to the embodiment illustrated in FIG. 17B. The set of these
blocks 80 can be coated with the electrically insulating coating
described above. According to one exemplary embodiment, the protective
component 30 can be formed by superimposing three blocks 80 separated by
electrodes 98. This protective component can have four poles, two of
which are electrodes 98, to achieve protection from overvoltages in
differential mode of a three-phase electrical installation.

[0134] According to another exemplary embodiment, the protective device
can have more than two terminals for connecting to the electrical
installation to be protected. Such an embodiment of the disclosure, for
example, corresponds to the use of the protective component 30 with a
number of poles greater than two such as the embodiment described with
reference to FIGS. 17A and 17B.

[0135] The characteristics described above, considered all together or in
any suitable combination as described, can produce devices for protecting
against surges that can meet both the IEC and UL standards, as well as
the UTE guide mentioned above. Each of these characteristics can,
independently of the others or in combination, be implemented in the
protective device according to the desired performance level. The
protective device can produce benefits from the advantages associated
with the characteristics previously described and that it incorporates.

[0136] These characteristics can be used to produce protective devices
provided for a nominal operating voltage of up to 690V, for example, in
alternating current under 50 Hz or 60 Hz and up to 895 V, for example, in
direct current and having protection from lightning strikes with a
nominal current (Imax) of 40 kA, for example, for a shock wave 8/20
according to the IEC standard and from lightning strikes with a nominal
current (In) of 20 kA for a shock wave 8/20 according to the UL standard.
These performances can be obtained with a single varistor chosen
appropriately. The maximum nominal voltage can easily be increased by
assembling one or several of these varistors serially.

[0137] Thus, it will be appreciated by those skilled in the art that the
present invention can be embodied in other specific forms without
departing from the spirit or essential characteristics thereof. The
presently disclosed embodiments are therefore considered in all respects
to be illustrative and not restricted. The scope of the invention is
indicated by the appended claims rather than the foregoing description
and all changes that come within the meaning and range and equivalence
thereof are intended to be embraced therein.